The present invention relates to a process intended to prevent deposition on the walls of metallurgical containers, particularly on the internal surfaces of the tap hole of these containers. It also concerns an improved metallurgical container which is suitable for carrying out the abovementioned process.
It is well known that the tap hole, especially of the distributor, represents a weak point in the chain of production using molten metal, more particularly in continuous casting processes. Various solutions have already been proposed, more particularly in the case of steel, as remedies for this problem,--see the papers, "Steel flow through nozzles: Influence of calcium", Faulring, Farrel and Hilty; Iron and steel-makers, February 1980, pages 14 to 20: and "Steel flow through nozzles: Influence of deoxidizers", Farrel and Hilty; Electric furnace proceedings AIME; Volume 29, 1971, pages 31 to 46 and GB-A-1 496 169; U.S. Pat. No. 3 848 072; PATENTS ABSTRACTS OF JAPAN, Vol. 7, no. 163 (M-229) (1308) and Vol. 9, no. 38 (M-358) (1761). It has thus been proposed to use self-eroding nozzles which prevent deposition of metallic materials, but which have to be replaced after relatively short operating periods and, besides, may influence the quality and the purity of the metallic bath.
It has also been proposed to clear the tap holes by means of oxygen lances.
Another means consists in using a nozzle which allows an inert gas to pass through and prevent direct contact between the molten metal and the walls of the tap hole and also avoid oxidation of the molten metal, this oxidation promoting the formation of deposits.
It has also been proposed to make additions of special substances to the molten metal, so as to make it more fluid and prevent deposition. Tests which were, in fact, conclusive have already been carried out with additions of calcium. In this case, however, it is essential to make the additions with great accuracy, depending on the previous treatment of the molten metal. Deoxidising agents have also been added, such as silica and manganese, aluminium, zirconium and titanium or rare earths. These rather chemical processes however affect the composition of the metal, in this case steel, and may prove to be relatively burdensome.
The aim of the present invention is to provide a process other than the mechanical and chemical processes mentioned, so as to prevent the formation of deposits on the walls of metallurgical containers.
Another aim of the present invention is to provide a process of the abovementioned type which does not exhibit the shortcomings of the processes of the state of the art, that is to say, a less costly process which depends to a lesser extent on the quality of the metal under treatment and on the treatment previously carried out and which is simple and easy to regulate.
The invention also aims at providing an improved metallurgical container which possesses an improved tap hole for enabling the process of the invention to be carried out.